Liquefied natural gas is stored at many locations throughout the world. The LNG is used when a local source of natural gas is not available or as a supplement to local and regional sources. Liquefied natural gas is typically stored at low pressure in the liquid state at cold temperatures. The LNG is usually pumped to a pressure that is slightly above the pressure of the natural gas distribution pipeline. The high pressure liquid is vaporized and sent to the pipeline. The vaporizers can use a fired heat source or use an energy efficient source of heat such as sea water or river water.
The submerged combustion LNG vaporizer (SCV) is a fired heat source type vaporizer used in LNG service. The conventional SCV includes a heat transfer coil installed in a liquid bath. The conventional vaporizer is equipped with submerged combustion burners firing into the liquid bath. The products of combustion are discharged into the bath. The discharge location is generally at a liquid submergence depth greater than two feet. The burner system includes a large high horsepower blower for providing combustion air. The submerged combustion burner provides heat, circulation, and turbulence for heat transfer.
There are many patents describing submerged combustion heat exchangers. The patents describe submerged pressurized products of combustion being bubbled through various combinations of holes and weirs to contact and heat water. The products of combustion are at a pressure sufficiently high to overcome the submergence depth. Deeper submergence depths require larger and higher horsepower combustion air blowers. In an application where the burner assembly discharges into water with an equivalent depth of 48 inches, the blower discharge pressure would need to be 48 inches water column plus the additional pressure drop of the system.
The submerged combustion heat exchanger disclosed in U.S. Pat. No. 3,368,548 utilizes submerged combustion burners firing into a heat exchange liquid bath containing a serpentine coil heat exchanger. The products of combustion from the high back pressure burners are used to provide heat exchanger liquid circulation within the bath for heat transfer with the serpentine coil.
In U.S. Pat. No. 3,138,150 a single burner discharges into a submerged down comer. The action of the products of combustion provides the heat transfer liquid upward circulation around a heat transfer coil.
U.S. Pat. No. 3,368,548 and 3,138,150 are typical of several submerged combustion heat exchangers where burners firing into a fluid provide fluid circulation around some type of heat transfer surface area.
These patents do not teach or suggest the products of combustion and water flow arrangement of this disclosure nor do they present the arrangement used to contact the products of combustion with the water flow nor do they teach the effective heat transfer arrangement to vaporize LNG as taught in this specification.